The present disclosure relates in general to optically pumped solid-state lasers that deliver laser radiation as a continuous wave or as a sequence of pulses. The disclosure in particular relates to systems and methods for providing low noise radiation of laser light through intracavity sum-frequency generation.
Low noise lasers are essential to progress in cutting edge scientific research such as carrier envelope phase stabilization, high precision optical clocks, and quantum control experiments in physics and chemistry. There are many other fields in which low noise lasers currently, or may in the future, find application.
Optically pumped, standing-wave, solid-state laser resonators are known in the art. Likewise, lasers using intracavity frequency doubling elements are known. A common problem observed with such lasers is significant noise generation in the output laser light, presumably due to interaction between intra-cavity harmonic and sum frequency generation. This chaotic behavior is often referred to as the “green problem”
One approach to addressing the green problem is limiting operation of the laser to single oscillation frequency. One method for producing single frequency operation is use of traveling wave laser cavity designs. However, such designs significantly increase the complexity and hence cost and challenges of manufacturing the lasers. Another approach to limiting operation to a single oscillation frequency is use of wavelength limiting elements in a standing wave oscillator. However, such wavelength limiting elements significantly reduce laser efficiency.
Another known approach to addressing the green problem is encouraging a relatively large number of longitudinal modes (operating wavelengths), such as on the order of 10 or more, and averaging the output to obtain a reduced-noise output beam. However, to generate large number of axial modes a relatively long resonator cavity is required, limiting the compactness of the laser design. The nature of the noise averaging depends on the randomness of the phase relationship of the axial modes. Typically, these types of lasers perform much worse than single frequency laser.
Still other approaches to addressing the green problem, but with a shorter laser resonator and a smaller number of modes, have been demonstrated. However, these approaches all suffer from stability issues, in that a low noise output may be provided for a relatively short period of time, after which the noise level varies significantly with time.